1. Field of the Invention
The present invention relates to a liquid crystal cell for displaying images thereon which uses smectic liquid crystal such as ferroelectric or antiferroelectric liquid crystal and nematic liquid crystal, and to a method of manufacturing the same.
2. Description of Related Art
Liquid crystal cells in which one electrode plate having a seal member and the other electrode plate having spacer walls are overlapped on each other to form a cell gap between two electrode plates are known hitherto. The cell gap is filled with liquid crystal such as smectic liquid crystal.
An example of this kind of liquid crystal cells is shown in FIGS. 29 and 30. On one electrode plate, seal member 1 is formed, and on the other electrode plate, plural spacer walls 3 are formed in parallel to each other. Two plates are overlapped to form a cell gap therebetween. The seal member includes side seals 1c, end seal 1b and end portions 1a defining an opening for filling the liquid crystal into the cell gap. The parallel spacer walls 3 are formed in a display area, leaving side passages at both sides. In a process to fill the cell gap with the liquid crystal, the cell is placed in a vacuum chamber and the liquid crystal is dropped at the filling opening. Then, the cell is heated to soften the liquid crystal and to close the filling opening. Then, the vacuum chamber is released to an atmospheric pressure so that a pressure difference is created between the outside of the cell gap and the cell gap closed by the liquid crystal. Liquid crystal 2 is sucked into the cell gap by the pressure difference through the inner passages between spacer walls 3 formed in the display area and the side passages between side seals 1c and the display area. Liquid crystal 2 moves at speed A1 through the inner passages while it moves at higher speed A2 through the outer passages as shown in FIG. 29. This is because the gap in the outer passages is larger than that of the inner passages (the inner passages include a color filter layer while the outer passages do not) and wettability of the liquid crystal in the outer passages is higher than that of the inner passages. Therefore, the liquid crystal sucked in through the outer passages reaches end seal 1b faster than the liquid crystal sucked in through the inner passages. Then, the liquid crystal which has reached end seal 1b turns its flow direction toward the inner passages (this is referred to as "turn-around flow" hereafter) as shown by arrows B in FIG. 30. The turn-around flow of the liquid crystal collides with the liquid crystal flowing in the inner passage at lower speed A1. This causes turbulence in the flow of the liquid crystal, and orientation of the liquid crystal is disturbed. If the orientation is disturbed, uniformity of the display on the liquid crystal cell will be damaged.
It is conceivable to form a dummy color filter layer in the outer passages to make the cell gap difference smaller. However, it is difficult to completely eliminate the cell gap difference because the dummy color filter layer is usually formed on a black mask layer which intercepts light emitted through the outer passages. Moreover, it is difficult to equalize wettability both in the outer passages and the inner passages. The liquid crystal is sucked into the cell gap by two driving forces, that is, the pressure difference between the cell gap and the outside, and a force caused by capillary effect in a small gap. When the size of the liquid crystal cell is small, e.g., six inches in diagonal, the pressure difference is predominant as a driving force of the liquid crystal. When the size is large, e.g., seventeen inches in diagonal, the pressure difference is predominant at the beginning of the filling process and the force by the capillary effect takes over at the last part of the filling process. In either case, as long as the cell gap difference in the outer and inner passages and the wettability difference exist, the orientation of the liquid crystal is disturbed by the turn-around flow caused by the flow speed difference in the outer and inner passages.
A proposal to equalize the liquid crystal flow speed in the cell by controlling the pressure in the filling process has been made in JP-A-5-313110. However, it has been found out that it is difficult to equalize the flow speed both in the inner and outer passages.